The candidate is a mid-career Ph.D. epidemiologist interested in an academic research career. She seeks training and research experience in collaborative immunoepidemiologic methods. Helicobacter pylori, intestinal helminths and Mycobacterium tuberculosis are three of the most common chronic infections of the developing world. We hypothesize that combined infection with two or more of these agents alters host responses to individual infections resulting in different clinical outcomes. The objectives of this study are to (1) identify asymptomatic adults in San Francisco South Bay communities who have combinations of infections with Helicobacter pylori, intestinal helminths and/or Mycobacterium tuberculosis; (2) to conduct immunologic studies evaluating differential patterns of host immune response to chronic co-infection in untreated subjects; and (3) to evaluate immune and clinical responses post-treatment in a pilot sample of subjects with known sequence of eradication therapy. As part of an ongoing prospective study of H. pylori transmission in the South Bay Area, approximately 1000 adults (ages 18-45) will be screened for latent TB infection [LTBI], Helicobacter pylori (CagA+) and intestinal helminth infection using established screening tests. Based on these results, approximately 200 subjects with combinations of single and multiple infection, including a sample without target infections, will be selected for specialized immunologic studies. In this group, additional assessments will include medical history, testing for other major infections, and in a subset, gastric cytokine expression. We will compare baseline measures of cellular and humoral immunity, including Th-1 and Th-2 associated cytokine production, delayed-type hypersensitivity, species-specific antibody subclass responses and measures of gastric inflammation pre- and post-treatment of these agents, and assess intra- and inter-subject variabilities in time. Secondary aims of the study include characterization of regulatory T-cell activity associated with co-infection. We will also store specimens with linked epidemiologic data for possible use in future studies to assess variations in PBMC gene expression patterns. Studies characterizing the immuno-modulatory effects of co-infection with these organisms have implications for treatment intervention and vaccine development of great relevance to the health needs of U.S. foreign born and the developing world.